DE-OS No. 30 25 515 discloses a method and apparatus for controlling resistance welding by means of a piezo-electric acceleration measuring device which is fastened to at least one of the two electrode holders. Accelerations which occur are preferably measured parallel to the axis of the electrode holder. In this known method, the magnitude of the electric current for the welding process is adjusted to the largest possible value, but below the value causing so-called welding splatter. The accelerations which occur at the electrode holder and which reach characteristically high values when welding splatter occurs are measured during the welding process for the purpose of electric current adjustment. If such acceleration peaks occur, the welding process is either interrupted or the magnitude of the current for the next welding process is reduced.
In tests with piezo-electric or other acceleration measuring devices which furnish an electrical measuring signal for current control, it was found that during the welding process and presumably due to the large currents and the magnetic field connected therewith, disturbances of the measuring signal occur which simulate accelerations. Such acceleration measuring devices are therefore not suitable for controlling the current during the welding process, for instance, by means of a phase gating control.